Various electronic devices comprise power supplies that convert electricity from one form into another. For example, most computing devices, such as desktop computers, laptop computers, and personal digital assistants comprise power supplies that convert voltage into a form that can be used by the various components of the devices, such as central processing units (CPUs) or other processors. Conversion may comprise alternating current (AC) to direct current (DC) conversion, as well as DC to DC conversion. In the former case, AC voltage, for example from a wall outlet, is converted into DC voltage, which is used by the internal components of the electronic device. In the latter case, the DC voltage is reduced to a level required by the internal components.
Current power supplies comprise various discrete components, such as inductors and capacitors, that are separately manufactured and then mounted, for example, on a circuit board. Due to the aggregation of the various discrete components, such power supplies are relatively large and heavy. Although not necessarily a critical concern in terms of larger electronic devices such as desktop computers, the size and heft of conventional power supplies can be disadvantageous for some applications, such as mobile electronic devices.
System-on-chip (SOC) is an emerging trend of integrating all components of an electronic system including digital, analog, mixed-signal, communication, and sensor functions into a single integrated circuit. The proliferation of the SOC concept has generated interest in integrating power management into integrated circuit chips. Power SOCs that monolithically integrate all active and passive components using low-cost semiconductor manufacturing processes would provide an extremely attractive solution with significant improvement in performance, as well as an unprecedented reduction in board space, parts count, and time to market. Unfortunately, the development of power SOCs is seriously hindered by a few major technical barriers. One such barrier is development of a cost effective means of integrating inductors and transformers onto a silicon chip while achieving adequate performance in terms of inductance, DC series resistance, maximum saturation current, and quality factor (Q factor), which is the ratio of reactive impedance to equivalent series resistance (ESR), and therefore provides a measure of inductor performance.
Current research on integrated magnetics for power SOCs has predominantly focused on utilizing micro-electro-mechanical-system (MEMS) micromachining technology as a post-processing step after the completion of a chip (e.g., a complementary metal-oxide-semiconductor (CMOS) chip) containing all power switching devices and control circuitry. The high DC resistance (typically 0.5 to 5 ohms (Ω)) and poor Q factor (typically 3 to 8) of the MEMS inductors/transformers, however, severely limit the current handling capability and efficiency of the power SOC. Furthermore, the large increase of fabrication complexity and cost associated with the MEMS post-processing approach raises questions as to the feasibility of large scale commercialization of the power SOC.